This project involves protein p21, the GTP/GDP binding protein specified by the mammalian oncogene family, ras. The project is part of a long term objective to develop novel, p21-specific substrate analogs which can serve: (a) as probes of the normal cellular function(s) of p21 and its role in ras-specific carcinogenesis and neoplasia, and (b) as agents useful in selectively attacking and preventing ras-specific neoplastic disease in vivo. The project has the following specific aims. (I) To synthesize and develop agents which interfere with the capacity of p21s to react with guanine nucleotides in vitro. Experiments will exploit selected, pure p21s and the results of preliminary observations of p21 reactivity with novel N2-substituted guanine derivatives. Approaches include: (a) refinement and extension of structure-activity relationships of N2-substituents through the synthesis of base, nucleoside, and nucleoside monophosphate forms, and (b) the development of an appropriate analog structure which will allow cell penetration, obviate a need for metabolism, and facilitate selective reaction with the nucleotide binding site of oncogenic p21 in its active, membrane-associated biophase. (II) To screen existing analogs and analogs developed via Aim I for their capacity to selectively affect the behavior and replication of cultured cells afflicted with a ras-induced neoplastic phenotype. This aim will use human and rodent cells; the lines include selected, ras-active tumor cell lines, and established cell lines transformed with ras vehicles which specify mutant p21s. (III) To identify, among candidates originating in the work on Aims I and II, a selective agent which can be used in vivo in rodents either: (a) to prevent chemical induction of ras-specific neoplasia, or (b) to positively affect the course of neoplastic disease resulting from the administration of ras-specific neoplastic cells. Approaches include the application of agents to normal and to tumor-bearing mice and/or rats and the use of a methylnitrosourea-induced, ras-specific rat mammary carcinoma model.